The experiments proposed in section I will use several complementary ultrastructural histochemical techniques to study the distribution and character of anionic molecules in the basal lamina (BL) of capillaries of the CNS. The continuous capillaries of the blood-brain barrier (BBB) as well as the fenestrated capillaries of the choroid plexus and circumventricular organs (CVOs) will be studied and contrasted. A more complete knowledge of the chemical character of the various vascular BL in the CNS may lead to better treatment for vasogenic brain edema (VBE), which accompanies strokes and other acute CNS insults, and to a better understanding of capillary growth during development and repair of CNS injury. The experiments in Section II will use several different complementary ultrastructural techniques to further study the abundant, uniquely oriented smooth endoplasmic reticulum (SER) in the CNS endothelial cell. These studies should enable a more complete knowledge of the distribution this organelle within individual endothelial cells, in different segments of the vasculature, and at different stages of development, and further elucidate its physiological function as a site of Ca++ sequestration. This basic information is necessary before any hypothesis regarding the role of this unique organelle in endothelial cell function is put forward. The experiments in Section III will use tannic acid-aldehyde fixation, in conjunction with a particulate tracer, to study the nature of the vesicles of CNS endothelial also; specifically seeking evidence favoring a transendothelial vesicular shuttle. Endothelial vesicular transport has been proposed as one possible route for the transfer of solute and H20 into the brain in VBE, which accompanies stroke and other CNS insults. A more complete understanding of endothelial vesicles may provide a means for more rational therapy of VBE.